Despite 35 years of clinical trials, there has been little improvement in five-year survival rates with any chemotherapeutic regimen for the treatment of metastatic melanoma. Here, we demonstrate a previously unrecognized role for Abl kinases in melanoma cells. We found that c-Abl/Arg non-receptor tyrosine kinases are activated in primary melanomas and in melanoma cell lines, and promote proliferation, survival, cell-cell adhesion, migration, invasion, and lung colonization/metastasis. In addition, c-Abl/Arg promote matrigel invasion via STAT3 and MMP-dependent pathways; increase cell-cell adhesion; and dramatically induce degradation of a metastasis suppressor. Moreover, drugs targeting c-Abl/Arg and Raf/MEK/ERK pathways cooperate to decrease melanoma viability. Based on these novel findings, we hypothesize that c-Abl/Arg activate novel pathways that cooperate with B-Raf to promote melanoma cell-cell adhesion, migration, invasion, and metastasis. We propose a comprehensive hypothesis-driven experimental design that will establish Abl kinases as novel and exploitable drug targets for metastatic melanoma. Aim 1 will define molecular pathways by which Abl kinases promote cell-cell adhesion, migration, and invasion. To achieve our objective, we will combine biochemical, molecular, and cell biological approaches using RNAi, pharmacological inhibitors, constitutively active forms of c-Abl/Arg, rescue experiments, 2D/3D cell culture, and melanoma- endothelial co-cultures to identify migration, invasion, and cell-cell adhesion signaling pathways driven by c- Abl/Arg. Aim 2 will test the prediction that c-Abl/Arg cooperates with Abl-independent pathways (e.g. B-Raf) to promote melanoma cell-cell, adhesion, migration, and invasion. Finally, three complementary approaches will be utilized in Aim 3 to identify mechanisms by which c-Abl/Arg promote metastasis. A novel GEM model that develops metastatic UV-induced melanomas, and lung colonization and spontaneous metastasis xenograft models will be used to test the prediction that blocking c-Abl/Arg-dependent signaling pathways inhibits metastatic progression. We also will test whether B-Raf and c-Abl/Arg inhibitors cooperate to prevent metastasis of melanomas harboring B-Raf mutations. The data obtained from this proposal not only will allow us to gain insight into the fundamental mechanisms by which c-Abl/Arg drive invasion and metastasis, but also will lead to clinical studies testing the efficacy of c-Abl/Arg inhibitors for treating metastatic disease. PUBLIC HEALTH RELEVANCE: Melanomas are essentially untreatable if they metastasize because they are resistant to all known chemotherapeutic agents. This proposal will solidify Abl kinases as novel, druggable targets in melanoma by identifying mechanisms by which Abl kinases promote invasion, and metastasis; determining which type of melanomas contain active Abl kinases; and testing whether Abl inhibitors cooperate with B-Raf inhibitors to kill melanoma cells and prevent metastatic progression. Data obtained from this proposal are likely to lead to the initiation of a clinical trial to test these novel drug combinations for treatment of metastati disease. 1